Semiconductor processing frequently involves providing a photoresist layer over a substrate. Portions of the photoresist layer are subsequently exposed to light through a masked light source. The mask contains clear and opaque regions defining a pattern to be created in the photoresist layer. Regions of the photoresist layer which are exposed to light are made either soluble or insoluble in a solvent. If the exposed regions are soluble, a positive image of the mask is produced in the photoresist. The photoresist is therefore termed a positive photoresist. On the other hand, if the non-irradiated regions are dissolved by the solvent, a negative image results. Hence, the photoresist is referred to as a negative photoresist.
A difficulty that can occur when exposing photoresist to radiation is that waves of radiation can propagate through the photoresist to a layer beneath the photoresist and then be reflected back up through the photoresist to interact with other waves propagating through the photoresist. The reflected waves can constructively and/or destructively interfere with other waves propagating through the photoresist to create periodic variations of light intensity within the photoresist. Such variations of light intensity can cause the photoresist to receive non-uniform doses of energy throughout its thickness. The non-uniform doses can decrease the accuracy and precision with which a masked pattern is transferred to the photoresist. Accordingly, it is desired to develop methods which suppress radiation waves from being reflected by layers beneath a photoresist layer.
A method which has been used with some success to suppress reflected waves is to form an antireflective material beneath a photoresist layer. Antireflective materials are typically materials which absorb radiation and thereby therefore quench reflection of the radiation. Antireflective materials absorb various wavelengths of radiation with varying effectiveness. The number of materials available for use as antireflective materials is limited. Accordingly, it is desired to develop alternative methods of varying the wavelengths absorbed, and effectiveness with which the wavelengths are absorbed, for antireflective materials.
A particular type of antireflective coating material is a deposited antireflective coating (DARC). An exemplary DARC is SixOyNz, wherein x is from about 40 to about 60, y is from about 29 to about 45, and z is from about 10 to about 16. The DARC can comprise, for example, Si50O37N13. A DARC can be formed by, for example, chemical vapor deposition on a substrate at about 400° C. and under a pressure of from about 4 Torr to about 6.5 Torr, utilizing SiH4 and N2O as precursors. The DARC material can be deposited either with or without a plasma being present in a reaction chamber during the deposition. A typical goal in utilizing a DARC film is to reduce reflected radiation reaching an overlying layer of photoresist to less than 10% of incident radiation at the DARC film.
A prior art process utilizing a DARC material is described with reference to a semiconductive wafer fragment 10 in FIG. 1. Wafer fragment 10 comprises a substrate 12. Substrate 12 can comprise, for example, monocrystalline silicon lightly doped with a background p-type dopant. To aid in interpretation of the claims that follow, the term “semiconductive substrate” is defined to mean any construction comprising semiconductive material, including, but not limited to, bulk semiconductive materials such as a semiconductive wafer (either alone or in assemblies comprising other materials thereon), and semiconductive material layers (either alone or in assemblies comprising other materials). The term “substrate” refers to any supporting structure, including, but not limited to, the semiconductive substrates described above.
A gate dielectric layer 14, polysilicon layer 16, and silicide layer 18 are formed over substrate 12. Gate dielectric layer 14 can comprise, for example, silicon dioxide; polysilicon layer 16 can comprise, for example, conductively doped polysilicon; and silicide layer 18 can comprise, for example, tungsten silicide or titanium silicide. Layers 14, 16 and 18 are to be ultimately patterned into a transistor gate structure.
An antireflective coating layer 20 is provided over silicide layer 18, and a photoresist layer 22 is provided over antireflective coating layer 20. Antireflective coating layer 20 can comprise, for example, an inorganic layer such as SixOyNz. In practice the layer can be substantially inorganic, with the term “substantially inorganic” indicating that the layer can contain a small amount of carbon (less than 1%).
Silicide layer 18 is preferably subjected to an anneal to improve a crystalline structure and a conductivity of the silicide layer prior to utilization of the layer in a transistor gate. The anneal of silicide layer 18 can comprise, for example, a temperature of 850° C. and a pressure of 1 atmosphere for a time of 30 minutes.
DARC material 20 is typically provided over silicide layer 18 prior to the anneal to protect layer 18 from gaseous oxygen during the anneal. If gaseous oxygen interacts with layer 18 during the anneal, the oxygen can oxidize a portion of layer 18 and adversely effect conductivity of layer 18. Unfortunately, the anneal conditions can detrimentally influence optical properties of DARC material 20. Specifically, DARC material 20 has optical properties that can be described by a refractive index coefficient (n) and an extinction coefficient (energy absorption coefficient) (k). The anneal conditions which improve conductivity of silicide layer 18 can alter one or both of “n” and “k” of layer 20. A stoichiometry of the materials of layer 20 is typically carefully chosen to adjust “n” and “k” of the material to appropriate parameters which will substantially quench reflected radiation before the radiation reaches photoresist layer 22. The effect of the anneal conditions on “n” and “k” can push such parameters out of an optimum adjusted range. Accordingly, it is desired to develop methods of forming DARC materials wherein “n” and “k” of the materials will be resistant to anneal condition induced changes.